The 2001 Washington State Legislature directed the Institute to, “conduct a longitudinal study of long-term [mental health] client outcomes to assess any changes in client status at two, five, and ten years.” Every year, the state’s public mental health system serves about 120,000 individuals. To follow changes over time, this paper focuses on a cohort of 39,039 adults who received public mental health services in January 2004. At the end of four years, mental health consumers were classified into those that 1) received services continually (every month), 2) regularly utilized mental health services (every quarter), 3) had intermittent use of mental health services (breaks longer than three months), and 4) clients who received services and did not return (“leavers”). Using administrative data, we looked at utilization patterns by demographics (age, region, and sex), previous utilization of mental health services, diagnoses, Medicaid eligibility, and functioning and impairment. After highlighting factors associated with service utilization, we outline future reports in this series that will address outcomes for public mental health consumers.